1. Field of the Invention
The present invention relates to a power source apparatus of a controlling apparatus or the like, and more particularly to a direct current stabilizing power source apparatus having a main electric power source such as a commercial power source and a backup power source thereof.
2. Description of the Related Art
In a direct current stabilizing power source apparatus that is used in a controlling apparatus driven by a commercial power source, a battery backup function is often provided as a backup at the time of electric power breakdown or the like. In providing this backup function, various efforts such as reduction of the number of components are made in order to avoid complication of the circuit construction or scale increase of the circuit accompanying this complication. For example, in a direct current stabilizing power source apparatus of battery backup type disclosed in Japanese Patent Application Laid-Open No. 2002-325448, a pulse transformer is provided in which the first primary winding is connected to a commercial power source, and the second primary winding is connected to a backup battery, where the output voltage taken out from the secondary side is controlled to converge on a target value by periodically driving the switching elements respectively connected to the first and second primary windings. In this direct current stabilizing power source, the construction of the controlling unit is simplified by driving at the same controlling timing the switching elements respectively connected to the two primary windings.
In a conventional direct current stabilizing power source apparatus of battery backup type as disclosed in Japanese Patent Application Laid-Open No. 2002-325448, plural switching elements are driven at the same time, so that the switching loss at the time of normal operation, which is not the time of backup, is large. Also, a circuit construction is adopted in which a diode prevents an electric current from flowing backward into the battery by an electric power induced on the second primary winding while the commercial electric power is input into the first primary winding, so that a circuit for charging this battery must be separately provided.